The present invention relates to a microwave heating device, and in particular, a microwave heating device with a microwave heating element mounted on the surface of a heating dish on which food is placed inside a heating chamber.
Unexamined Japanese Patent Application Publication (A) S52-111046 discloses a conventional microwave heating device with a microwave heating element mounted on a heating dish. The conventional microwave heating device has a microwave heating element mounted on the bottom face of a metallic dish. The microwave heating element is heated by microwaves generated at the bottom side of the heating chamber, and the microwaves heat an object placed on the metallic dish.
The conventional microwave heating device insufficiently heats the object on the metallic dish. The object absorbs the microwaves directly while the surface of the object that contacts the face of the dish is heated intensely and burns. Therefore, the conventional microwave heating device does not satisfy the basic objective of microwave heating, i.e., to heat the inside of the object.
The conventional microwave heating device also can heat the object directly with microwaves when the dish is removed from the heating chamber. However, this method of heating an object suggests that it is necessary to move the object being heated to another container while cooking to be able to heat the object directly by microwaves after having been heated on the dish provided with the microwave heating element. This method of heating an object requires a more complicated operation for the user and a longer cooking time.
The present invention provides a microwave heating device capable of heating both the surface and the inside of the object with a simple and quick operation.
The microwave heating device according to the present invention includes a heating chamber for placing an object to be heated; a magnetron for generating microwaves; a waveguide for supplying the microwaves generated by the magnetron through the bottom of the heating chamber; a heating dish on which the object to be heated is placed; a microwave heating element positioned on the bottom surface of the heating dish to generate heat by absorbing microwaves; and an access passage for allowing the microwaves supplied by the waveguide to reach above the heating dish from below the heating dish.
The object on the heating dish is heated by the heating dish, which is heated by the microwave heating element and by microwaves that reach above the heating dish. Therefore, the surface and the inside of the object can be heated in a simple and quick heating operation. The heating chamber can have recessed areas for providing gaps between the inner wall of the heating chamber and the heating dish, particularly in areas of the inner wall adjacent to the heating dish. Therefore, microwaves that are not absorbed by the microwave heating element can be sent upward to efficiently reach areas above the heating dish through the gaps between the heating dish and the recessed areas.
The heating dish can have the microwave heating element included on any surface of the heating dish except on the outer edge of the heating dish. Therefore, both the microwave heating element and the microwaves can more efficiently heat the object by sending the microwaves to the outer edge of the heating dish where it is less likely that object is present. The safety of the device also improves since the outer edge of the heating dish is heated less, and the outer edge is where users tend to hold the heating dish.
The microwave heating device of the present invention can also have a heater provided above the heating dish. Therefore, the surface of the object can be heated to a desirable temperature.
The dimension of the access passage in the direction perpendicular to the traveling direction of the microwaves can be greater than one quarter of the wavelength of the microwaves. Therefore, the microwaves can be sent more effectively above the heating dish.
The microwave heating device can have a first surface on the inner wall of the heating chamber and a second surface facing a different direction from the first surface. The first and second surfaces can have rails for supporting the heating dish, and these rails can have a plurality of members which are properly spaced from each other on a single plane. Therefore, more microwave energy can be efficiently sent through the gaps between the members of the rails.
The microwave heating device can have a groove on the outer edge of the surface of the heating dish that can carry the object to be heated. Therefore, the cooking process can be improved since any water or oil released from the food can be carried away by the groove and separated from the food.
The lowest part of the heating dish can be located below the microwave heating element. Therefore, if the heating dish is placed on a table or the like, the microwave heating element, which can reach a very high temperature, is prevented from touching the table.
The microwave heating device can also have a rotating antenna that rotates to spread the microwaves in the waveguide inside the heating chamber and a rotation control unit for controlling the rotation of the rotating antenna. The rotation control unit can be capable of stopping the rotating antenna at a position corresponding to the height at which the heating dish is stored when the magnetron generates microwaves. Therefore, various types of cooking can be achieved with the heating dish.
The area of a surface of the microwave heating element of the heating dish perpendicular to the traveling direction of the microwaves can be equal to the area of the rotating antenna when the distance between the heating dish and the bottom face of the heating chamber in the traveling direction of the microwaves is xe2x85x9 of the wavelength of the microwaves. The area can increase in proportion to the distance in the traveling direction when it is greater than xe2x85x9 of the wavelength of the microwaves and can decrease in proportion to the distance in the traveling direction when it is smaller than xe2x85x9 of the wavelength of the microwaves. Therefore, various types of cooking can be achieved with the heating dish.
The heating dish can be stored in the heating chamber at a distance of xe2x85x9 of the wavelength of the microwaves apart from the bottom face of the heating chamber. Therefore, the object can be cooked on the heating dish more efficiently using the microwave heating element.
The rotating antenna inside the heating chamber can rotate within a specified plane to spread the microwaves in the waveguide and can have metal plates on the circumference of the rotating antenna. An antenna enclosure can be located near the connection between the waveguide for enclosing the rotating antenna so that when a placement span, which is a distance between the circumference of the rotating antenna and the surface of the antenna enclosure along a direction perpendicular to the specified plane, is not uniform, the metal plates are positioned in areas where the placement span is the longest. Therefore, the circumference of the heating dish is prevented from being overheated to cause fluctuations in heat over the heating dish, because the microwaves that travel toward the side wall of the heating chamber relatively further away from the circumference of the rotating antenna will be guided by the metal plates toward the center of the heating chamber.
The tip of the metal plates can be located ahead of the rotating antenna relative to the traveling direction of the microwaves. Therefore, the metal plate can correct the traveling direction of the microwaves that are supplied to the heater chamber via the rotating antenna. The microwave heating device can have a heater on the circumference of the rotating antenna so that the metal plates are located between the heater and the rotating antenna. Therefore, the heater will not interfere with the rotating antenna""s guidance of the microwaves in the desired direction.
The microwave heating device can have a door that controls access to the heating chamber and a first protruding part on the inner wall of the heating chamber, which protrudes into the heating chamber and abuts against the heating dish when the heating dish is placed in an undesirable position for the supply of microwaves to the heating chamber. The magnetron generates microwaves only when the door is closed, and abutting the heating dish against the first protruding part prevents the door of the heating chamber from closing. Therefore, the microwaves can be prevented from being supplied to the heating chamber while the heating dish is placed in an undesirable position for supplying microwaves to the heating chamber. For example, an undesirable position can be a place in which the heating dish tends to cause electric discharges between the heating dish and the rotating antenna.
The microwave heating device can also have a heater for heating foods in the heating chamber; a metallic dish in the heating chamber for carrying the object to be heated when it is heated by the heater; and a second protruding part that abuts against the metallic dish when the metallic dish is placed in an undesirable position in the heating chamber. The magnetron generates microwaves only when the door is closed so that when the metallic dish abuts against the second protruding part, the door of the heating chamber is prevented from closing. The heating dish is shaped so that it does not abut against the second protruding part even when the heating dish is located in every possible position in the heating chamber. Therefore, the metallic dish is prevented by the second protruding part from being placed in the heating chamber when microwaves are supplied to the heating chamber. However, the second protruding part does not prevent the heating dish from being installed in the heating chamber.
The microwave heating element can have a thickness that equalizes the amount of microwaves absorbed by the microwave heating element with the amount of microwaves that are passed through. Therefore, the microwave heating element mounted on the heating dish can efficiently exchange the heat generated by absorbing the microwaves.